KR100626002B1 - Manufacturing method of thin film transistor and flat display device employing the thin film transistor manufactured by the method - Google Patents

Abstract

The present invention comprises the steps of forming an amorphous silicon film on a substrate; Crystallizing the amorphous silicon film to form a polysilicon film; First etching the surface of the polysilicon film with a silicon oxide etching solution; And second etching the surface of the first etched polysilicon film with a polysilicon etching solution, and a flat panel display device having the thin film transistor manufactured according to the method. do. According to the method of manufacturing the thin film transistor of the present invention, the height of the surface protrusion of the polysilicon film formed by crystallizing the amorphous silicon film is reduced, thereby improving the interfacial characteristics with the gate insulating film formed thereon as the surface is planarized, A semiconductor active layer in which damage is suppressed can be obtained. By using the thin film transistor obtained by this method, it is possible to obtain a flat panel display having improved reliability.

Description

Manufacturing method of thin film transistor and flat display device employing the thin film transistor manufactured by the method

1 is a cross-sectional structural view of an embodiment of a thin film transistor manufactured according to the present invention,

2 is a partial cross-sectional view of an EL display device having a polysilicon film according to an exemplary embodiment of the present invention.

<Short description of drawing symbols>

1 ... substrate 2 ... buffer layer

3 ... gate insulating film 4 ... interlayer insulating film

12 ... semiconductor active layer 13 ... gate electrode

14 Source electrode 15 Drain electrode

The present invention relates to a method for manufacturing a thin film transistor, and more particularly, to a method for manufacturing a thin film transistor using a polysilicon layer as a semiconductor active layer, and a thin film transistor obtained by the method and a flat panel display device having the same.

The polysilicon film used as the channel layer of the thin film transistor can be obtained by crystallizing the amorphous silicon film using various crystallization methods. Among the crystallization methods of the amorphous silicon film, the crystallization method using a laser is widely used because it has a relatively low thermal effect on an insulating substrate such as a glass substrate and can form polysilicon having superior physical properties as compared to the solid phase crystallization method. It is becoming.

However, in the crystallization method using a laser, the density difference generated when the silicon liquid phase changes to a solid phase becomes uneven, so that surface projections are generated in a portion where crystallization is relatively slow, resulting in poor surface roughness of the polysilicon film. Has disadvantages. The formation of such protrusions is unavoidable in the crystallization step of crystallizing the amorphous silicon film into the polysilicon film by the laser crystallization method, which causes various defects in subsequent steps. For example, when depositing the metal material for the gate insulating film and the gate electrode on the polysilicon film, the metal material for the gate insulating film and the gate electrode is deposited along the surface protrusion of the polysilicon, so the metal material for the gate insulating film and the gate electrode is poly It has a projection similar to the surface projection of the silicon film. As described above, in the gate insulating layer having the protrusion, the breakdown voltage may be lowered and the leakage current may increase due to the protrusion. In addition, if the metal material for the gate electrode on which the protrusion is formed is hillocked due to poor surface roughness of the metal material for the gate electrode, the device material is degraded. In addition, these protrusions cause non-uniformity in the etching process and the exposure process, leading to a decrease in reliability of the device.

In order to solve the above problems, a method of removing the surface protrusions of the polysilicon film by wet oxidation to oxidize the surface of the polysilicon film and then repeatedly performing the HF treatment has been proposed. According to this method, since several surface oxidation and HF treatment processes are performed, there is a problem that polysilicon films other than the projections are also lost.

As another method for improving the surface roughness of the polysilicon film, a method of sequentially isotropic etching and anisotropic etching of the polysilicon film surface has been proposed (Japanese Patent Laid-Open No. 5-299396).

By the way, when surface treatment is performed according to the etching method of the polysilicon film known to date, the surface roughness characteristic of the polysilicon film is not enough or the polysilicon film other than the projection part is lost, and there exists a problem that process reliability falls.

Accordingly, the technical problem to be achieved by the present invention is to solve the above-mentioned problems and to minimize the damage of polysilicon crystals and to reduce the height of the surface protrusions. It is to provide a flat panel display device.

In order to achieve the above technical problem, the present invention comprises the steps of forming an amorphous silicon film on the substrate;

Crystallizing the amorphous silicon film to form a polysilicon film;

First etching the surface of the polysilicon film with a silicon oxide etching solution; And

And etching the surface of the first etched polysilicon film with a polysilicon etching solution.

Another technical problem of the present invention is an active layer formed by patterning a polysilicon film prepared according to the above method;

A gate electrode insulated from the active layer; And

And a thin film transistor including a source and a drain electrode electrically connected to the active layer.

According to another aspect of the present invention, there is provided a flat panel display device including the above-described thin film transistor in each pixel, and a pixel electrode connected to a source electrode or a drain electrode of the thin film transistor.

The present invention provides a surface treatment method of a polysilicon film that can remove the surface protrusion of the polysilicon film or reduce the height of the surface protrusion, and the method thereof will be described in detail.

An amorphous silicon film is formed on the substrate. The method of forming the amorphous silicon film is not particularly limited, and for example, a chemical vapor deposition method can be used.

The thickness of the amorphous silicon film formed on the substrate is preferably 450 to 530 kPa. If the thickness of the amorphous silicon film exceeds 530 kPa, the polysilicon film is formed nonuniformly, and if the thickness of the amorphous silicon film is less than 450 kPa, the polysilicon film is formed nonuniformly.

Next, the amorphous silicon film is crystallized to form a polysilicon film.

As a non-limiting example of the method of crystallizing the amorphous silicon film, there is a crystallization method using a laser. Examples of crystallization methods using lasers include laser annealing such as Excimer Laser Annealing (ELA method). According to the conventional ELA method, when a pulse laser of 20 to 200 nsec is irradiated to the amorphous silicon film, the amorphous silicon is melted and polysilicon crystals are formed in the process of cooling it.

Protrusions are formed on the surface of the polysilicon film around crystal grain boundaries, and silicon oxide films are naturally formed in a portion of the surface of the polysilicon film under a crystallization process or in an air atmosphere. The silicon oxide film thus formed has a thickness of 10 to 100 GPa, particularly about 70 GPa.

The surface of the polysilicon film as described above is subjected to primary etching with a silicon oxide etching solution to selectively remove the silicon oxide film formed in the crystallization process or in the air. At this time, as the silicon oxide etching solution, as an etching solution capable of selectively etching only silicon oxide, HF aqueous solution may be mentioned as a specific example thereof. The concentration of the HF aqueous solution is not particularly limited, but may be 0.01 to 15% by weight, preferably 0.1 to 1.0% by weight, especially about 0.5% HF aqueous solution.

The first etching time using the silicon oxide-based etching solution may be performed for 10 to 200 seconds, preferably 50 to 100 seconds. If the primary etching time exceeds 200 seconds, the lower substrate can be etched, and if it is less than 10 seconds, it is unfavorably etched unevenly.

Thereafter, the surface of the polysilicon film subjected to the primary etching treatment is subjected to secondary etching using a polysilicon etching solution.

The polysilicon etching solution is an etching solution capable of selectively etching only polysilicon, and specific examples thereof include an aqueous solution of nitric acid. The concentration of the aqueous nitric acid solution is not particularly limited, but it is preferable to use 90 to 100% by weight, preferably 99.3 to 100% by weight nitric acid solution.

Secondary etching time using the polysilicon etching solution is variable depending on the etching solution and its concentration. In example embodiments, the etching may be performed at a level substantially equal to a first etching time using the silicon oxide-based etching solution.

According to the method of manufacturing the thin film transistor of the present invention, the height of the surface protrusions present on the surface of the polysilicon film is reduced as compared with the case of using a conventional etching method, and the height of the surface protrusions is 40 nm or less, preferably 20 to 30 nm. to be. If the height of the surface protrusion of the polysilicon film exceeds 40 nm, it is not preferable to reduce the breakdown voltage of the upper insulating film.

In addition, according to the manufacturing method of the present invention, if only the silicon oxide is selectively etched when the surface of the polysilicon film is etched, then the polysilicon etching is performed to prevent the polysilicon is unnecessarily etched, and the process reliability can be prevented.

FIG. 1 illustrates a cross-sectional structure of a thin film transistor manufactured by polysilicon film surface treatment according to an embodiment of the present invention.

Referring to FIG. 1, a buffer layer 2 is formed on a substrate 1 such as a glass substrate. The gate insulating film 3 is provided on the buffer layer 2, and the gate electrode 13 is formed of a conductive metal film on a predetermined region of the gate insulating film 3. The gate electrode is formed of a conductive metal film such as MoW, Al, Cr, Al / Cu, but is not limited thereto. The region where the gate electrode 13 is formed corresponds to the channel region C1 of the active layer 12. An interlayer insulating film 4 is formed on the gate electrode 13, and the source electrode 14 and the drain electrode 15 are formed in a state where contact holes are formed in the interlayer insulating film 4 and the gate insulating film 3. It is formed on the interlayer insulating film 4.

The thin film transistor manufactured according to the thin film transistor manufacturing method of the present invention can be usefully used in flat panel display devices. The flat panel display includes, for example, a CRT display device such as a color display tube (CDT) or a color picture tube (CPT), a plasma flat panel display, a liquid crystal display, an electroluminescent display, and the like.

Referring to FIG. 2, an electroluminescent device including a thin film transistor according to an embodiment of the present invention is as follows.

Referring to FIG. 2, a buffer layer 120, a polysilicon layer 130, a gate electrode layer 150, a source / drain electrode layer 170a and b, which are semiconductor active layers, may be disposed on one surface of the substrate 110. A TFT layer composed of an insulating layer, such as the gate insulating layer 140 and the intermediate layer 160, may be disposed. The passivation layer 180 is formed on one surface of the source / drain electrode layers 170a and b, and the first electrode layer 190 is disposed through the via hole 181 formed on one side of the passivation layer 180. The pixel defining layer 191 may be formed on the passivation layer 180, and an opening region 194 is disposed in the corresponding region on the first electrode layer 190. An electroluminescent part 192 including a light emitting layer or the like may be formed on one surface of the first electrode layer 190 as the opening region 194, and the second electrode layer 193 may be entirely deposited on the top surface thereof. In the electroluminescent display device, the semiconductor active layer 130 through which the channel is energized by an electrical signal applied to the gate electrode 150 is formed of a polycrystalline polysilicon film surface-treated according to the present invention.

As described above, the thin film transistor of the present invention may be applied to all flat panel display devices including a liquid crystal display, and may have a structure in which a pixel electrode is connected to a source / drain electrode of the thin film transistor.

Hereinafter, the present invention will be described with reference to the following examples, but the present invention is not limited only to the following examples.

Example 1

First, a silicon oxide film was formed as a buffer layer on a glass substrate. Amorphous silicon was chemically vapor deposited on the buffer layer to form an amorphous silicon film having a thickness of 500 kHz.

Laser annealing was performed on the amorphous silicon film under nitrogen atmospheric pressure to form a polysilicon film.

The polysilicon film was first etched for 100 seconds using a 0.5 wt% HF aqueous solution, which is a silicon oxide etching solution.

Subsequently, the polysilicon film after the primary etching was subjected to secondary etching for 1 minute using a 99.4% by weight aqueous solution of nitric acid as a polysilicon etching solution to form a thin film transistor.

Comparative Example 1

A thin film transistor was formed in the same manner as in Example 1 except that the primary and secondary etching of the polysilicon film were not performed.

In the said Example 1 and the comparative example 1, the surface state after primary etching and an etching process was observed using the electron scanning microscope (SEM).

As a result, it was found that the height of the surface protruding portion on the upper part of the polysilicon film of Example 1 was lower than in the case of Comparative Example 1.

According to the method of manufacturing the thin film transistor of the present invention, the height of the surface protrusion of the polysilicon film formed by crystallizing the amorphous silicon film is reduced, thereby improving the interfacial characteristics with the gate insulating film formed thereon as the surface is planarized, A semiconductor active layer in which damage is suppressed can be obtained. By using the thin film transistor obtained by this method, it is possible to obtain a flat panel display having improved reliability.

Claims (7)

Forming an amorphous silicon film on the substrate; Crystallizing the amorphous silicon film to form a polysilicon film; First etching the surface of the polysilicon film with a silicon oxide etching solution; And And etching the surface of the first etched polysilicon film with a polysilicon etching solution. The method of manufacturing a thin film transistor according to claim 1, wherein the silicon oxide etching solution is HF aqueous solution. The method of claim 1, wherein the polysilicon etching solution is an aqueous solution of nitric acid. The method of claim 1, wherein a crystallization method using a laser is used to crystallize the amorphous silicon film. An active layer formed by patterning a polysilicon film prepared according to any one of claims 1 to 4; A gate electrode insulated from the active layer; And And a source and drain electrode electrically connected to the active layer. The thin film transistor according to claim 5, wherein the height of the surface protrusion of the polysilicon film is 20 to 40 nm. A flat panel display device comprising the thin film transistor of claim 5 in each pixel, and a pixel electrode connected to a source electrode or a drain electrode of the thin film transistor.

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